(1) Field of the Invention
This invention relates to industrial ballistic tools, and more particularly to ammunition therefor.
(2) Description of the Related Art
Industrial ballistic tools are used in a variety of applications. One common application is the in situ cleaning of kilns, for which the tools are commonly identified as kiln guns. Additional applications lie in the tapping and cleaning of furnaces, the cleaning of copper smelters, the cleaning and clearing of silos, the cleaning of boilers, and the like.
By way of example, rotary kilns, which are used to calcine cement and lime, are typically 3 to 7 meters in diameter and 30 to 150 meters long. Calcining takes place at elevated temperatures, typically in the range of 1100xc2x0 C. to 1500xc2x0 C. During the calcining process, because of many processing variables, the product may adhere to the sidewall of the kiln forming a clinker, ring or dam. If this adherent obstruction is not removed, additional product will accumulate, reducing or stopping throughput. Removal of the obstruction is necessary.
It is not economically feasible to stop the kiln to remove the obstruction. Also, considering that the ring may form 5 to 10 meters from the end of the kiln, it is not safe or efficient for an operator to attempt to manually remove the obstruction with a long pole or by like methods. Thus many users of rotary kilns utilize industrial ballistic tools. A tool operator will position the tool in a kiln port and then fire metallic projectiles at the obstruction. Impact of the projectiles with the obstruction removes the obstruction from the sidewall of the kiln. The metallic projectiles are usually formed from lead, a dense material with a relatively low vaporization (boiling) temperature of 1750xc2x0 C. The lead projectiles knock clinkers from the kiln sidewall and then fall into the kiln and may be vaporized.
Industrial ballistic tools are also utilized by manufacturers of steel, ferrosilicon and other materials. Prior to casting these metals, molten metal is typically contained within an electric furnace sealed by a carbon or clay base plug. Since the molten metal is at a temperature in excess of 2500xc2x0 C., manual removal of the plug is not feasible. One way that the plug may be removed is with an industrial ballistic tool. A metallic projectile is fired from the industrial ballistic tool to break open the plug, starting the flow of molten metal. To prevent contamination of the metal, the projectile typically is formed of a material such as lead that will vaporize on contact with the molten metal after rupturing the plug.
Due to environmental concerns, lead is being phased out as a projectile material for use with industrial ballistic tools. Zinc and zinc alloys have also been utilized as lead substitutes. Their relatively low density may make them disadvantageous for certain uses. A ballistically stabilized zinc-based projectile is described in U.S. Pat. No. 5,824,944 of Jack D. Dippold et al.
Additionally, when repeated firing heats the tool chamber, the plastic tubes of many existing industrial shells may melt and/or leave a residue. The residue may deleteriously affect the firing of subsequent rounds.
In other fields, so-called xe2x80x9cbulletless ammunitionxe2x80x9d has been developed. Cartridges without bullets or other substantial projectiles have been utilized as xe2x80x9cblanksxe2x80x9d or to propel grenades and the like. However, U.S. Pat. No. 3,621,781 discloses bulletless ammunition in which the sidewall of a spent cartridge becomes the projectile propelled by the charge of the subsequent cartridge. In the small arms field, substantial developments in such bulletless ammunition technology were made by Douglas Olson. These include use of cut down brass rifle cases as the case/projectile for use in revolvers and autoloaders. These are discussed in Karwan, C. Hollowpoinp Bulletless Ammo, Hi-Tech Firearms, Petersen Publishing Co., (October, 1998), pp. 65-68.
Accordingly, in one aspect, the invention is directed to ammunition for use with a discharging apparatus which has a chamber for receiving the ammunition, a muzzle, and a barrel between the chamber and the muzzle. The ammunition includes a case comprising in major part zinc and extending aft-to-fore from a base to a mouth and having interior and exterior surfaces. A propellant charge is carried within the case. An over-powder member cooperates with the case to enclose the propellant charge. The ammunition lacks a projectile within the case in a location effective to be expelled from the apparatus and having a mass in excess of a mass of the case.
In various implementations, the case may be a unitary casting of a zinc alloy. The case exterior surface may have at least eight circumferential grooves, the grooves occupying a total of at least about 25% of a length of the case. The plurality of grooves may have widths of between 0.9 mm and 1.8 mm, peak depths of between 0.08 mm and 0.30 mm from a maximum case diameter and, along with interspersed ungrooved areas, extend along at least 70% of the case length. The peak depths may be between 0.13 mm and 0.23 mm and the widths between 1.1 mm and 1.5 mm. The interspersed ungrooved areas may have diameters within 0.05 mm of the maximum case diameter. The ammunition may be combined with an industrial ballistic tool barrel having rifling with a land-to-land diameter which is 0.943-0.950 in. (2.395-2.413 cm) and a groove-to-groove diameter which is 0.954-0.960 in. (2.423-2.438 cm). The case exterior surface may have a circumferential extractor groove having a depth of at least 1 mm and separated by no more than 2 mm from an aft extremity of the case. The ammunition may further include a primer. The primer may comprise a metallic cup mounted in the case base. The primer maybe a #209 primer. The case may have a mass of between 70 g and 10 g, a length of between 50 mm and 65 mm, and a maximum diameter of between 20 mm and 26 mm. The over-powder member may be a plug or it may be a cap which extends from a rear rim to a front end and has a rear portion encircling a fore portion of the case. The cap may be formed of a resinous polymer. The case fore portion may include a flange having an external flange diameter. The cap rear portion may include an inwardly directed part aft of the flange and having an external diameter less than the flange diameter so as to cooperate with the flange to resist forward translation of the cap relative to the flange. A cap length may be between 100% and 3000% of a case length. There may be a first radial clearance of at least 1.0 mm between the flange and the cap. There may be a second radial clearance of between interference fit and 0.5 mm between the cap inwardly directed part and a neck portion of the case aft of the flange.
In another aspect, the invention is directed to ammunition for use with a discharging apparatus including a chamber for receiving the ammunition, a muzzle, and a barrel between the chamber and the muzzle. The ammunition extends from a rear end to a front end and includes a metallic case. The case extends aft-to-fore from a base at the ammunition rear end to a mouth and has interior and exterior surfaces. A cover is formed of a polymeric resin and extends from a rear rim to a front end at the ammunition front end. The cover has a mass not in excess of the mass of the case and has interior and exterior surfaces. The ammunition further includes a propellant charge advantageously confined within at least one of the case and cover.
In various implementation, the case may have a central longitudinal channel extending forward from the primer pocket at the base to a fore portion proximate the mouth. A primer may be mounted within the primer pocket. The propellant charge may be confined within a volume at least partially defined by the central longitudinal channel and the cover interior surface. The cover may have a cover length and the case may have case length less than the cover length. The cover may consist essentially of injection molded high density polyethylene and the case may consist essentially of die cast zinc or zinc alloy. The cover interior surface may have a circumferential recess forward of the case and effective to locally weaken the cover. The weakening is sufficient to permit internal pressure within the cover to sever a portion ahead of the recess from a portion behind which remains attached to the case when the ammunition is fired. The recess may have a longitudinal extent of between 1 mm to 5 mm and may locally thin the cover to a minimum thickness of between 0.6 mm and 1.4 mm from an adjacent thickness of between 1.6 mm and 2.6 mm. The case may have a mass of between 70 g and 10 g, a length of between 30 mm and 40 mm, and a maximum diameter of between 20 mm and 26 mm. The case exterior surface may have a plurality of circumferential grooves, the grooves occupying a total of at least about 25% of a length of the case.
In another aspect, the invention is directed to a method for operating an industrial ballistic tool to discharge a plurality of ammunition rounds. A plurality of ammunition rounds are provided each comprising a zinc case and a charge of propellant. A first such round is inserted into a chamber of the tool. Ignition of the charge of the first ammunition round is caused. A second such ammunition round is inserted into the chamber. Ignition of the charge of the second ammunition round is caused so as to expel the spent case of the first ammunition round out of the muzzle at an effective muzzle kinetic energy.
In various implementation of the invention, the second round insertion and ignition may be repeated, each time utilizing a new ammunition round to expel the case of the previously-discharged round. Prior to insertion of the first round, a chargeless case may be inserted into the chamber so that the insertion of the first round advances the chargeless case toward the muzzle. Prior to insertion of the first round, a preliminary round may be inserted into the chamber. The charge of the preliminary round may not be ignited and insertion of the first round advances the preliminary round toward the muzzle. Alternatively, the charge of the preliminary round may be ignited and insertion of the first round advances the spent case of the preliminary round toward the muzzle. The muzzle kinetic energy may be at least 10 kJ. Insertion of the second round may include engaging an aft end of the spent case of the first round with a fore end of the second round so as to advance the spent case toward the tool muzzle. The ignition of the charge of the second ammunition round may include permitting a first portion of a non-metallic cover portion of the second ammunition round to separate from a remaining second portion and travel behind the spent case of the first ammunition round. This may further comprise permitting the remaining second portion to seal against the chamber to resist combustion gas leakage around the case of the second round.
The present invention may facilitate a number of advantages over prior art slugs. A key potential advantage is cost. Beyond manufacturing cost, costs of collection and disposal of spent hulls is eliminated. Another advantage is that use of a metal case does not entail the melting associated with plastic tubes of conventional industrial ammunition. This may increase reliability.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.